Mounting method for core internals

ABSTRACT

An old core shroud ( 11 ) and an old jet pump ( 16 ) received in a reactor pressure vessel ( 1 ) are cut and carried out. A module of core internals having a new core shroud (N 11 ), a new jet pump (N 16 ) and a new baffle plate (N 29 ) integrated is carried into the reactor pressure vessel ( 1 ) in which an old baffle plate ( 28 ) and an old shroud support cylinder ( 13 ) welded and fixedly secured to the reactor pressure vessel ( 1 ), and an old shroud support leg ( 12 ) fixedly secured to said old baffle plate ( 28 ) and said old shroud support cylinder ( 13 ) are left. Then, the new baffle plate ( 29 ) is fixedly secured to the old baffle plate ( 28 ), and the new core shroud ( 11 ) is fixedly secured to the old shroud support leg ( 12 ).

TECHNICAL FIELD

The present invention relates to a mounting method for core internalsfor mounting core internals such as a core shroud in a reactor pressurevessel received in a reactor building of a nuclear power plant, and moreparticularly to a mounting method for core internals suitable for usewhen core internals are replaced.

BACKGROUND ART

In the past, when the core shroud as core internals or the like isreplaced, an old core shroud and old core internals such as a jet pumpare cut and disassembled, and carried out, after which a new core shroudand new core internals such as a jet pump are individually carried intoa reactor pressure vessel (hereinafter called “RPV” (Reactor PressureVessel), and they are mounted by welding or the like, as described in,for example, Japanese Patent Laid Open No. Hei 8 233972, Japanese PatentLaid Open No. Hei 8 152495, or Japanese Patent Laid Open No. Hei 10132985. The shroud is carried-in in the form divided into two parts orsingly, and the jet pump is singly carried-in in the form of a jet pumpinlet mixer, a jet jump riser, and a jet pump diffuser.

Further, there has been known an integral construction of core internalssuch as a core shroud and a jet pump, as described in, for example,Japanese Patent Laid Open No. Hei 6 281776.

DISCLOSURE OF INVENTION

The core shroud is for output of 800 Mwe, and has a weight of about 40tons, a diameter of about 5 m, and a length of about 7 m. In order tocarry the core shroud into a reactor building operating floor through alarge article carrying in hatch, there are a case of interfering with adimension of the large article carrying in hatch and a case where thecapacity of a ceiling crane in the reactor building is short. Therefore,it is necessary to divide and carry in them, as described in JapanesePatent Laid Open No. Hei 8 233972, Japanese Patent Laid Open No. Hei 8152495, or Japanese Patent Laid Open No. Hei 10 132985, posing a problemthat a term of work for replacing the core shroud becomes long.

Further, since with respect to the jet pump, its constituent parts, 20jet pump inlet mixers, 10 jet pump risers, and 20 jet pump diffusershave been singly carried in, a worker moves into the core to assemblethem, which requires measures such as installation of a core internalsshield, thus posing a problem that a term of work for replacementbecomes long.

That is, in the conventional systems described in Japanese Patent LaidOpen No. Hei 8 233972, Japanese Patent Laid Open No. Hei 8 152495, orJapanese Patent Laid Open No. Hei 10 132985, there encountered a problemthat a term of work for replacement of core internals is extended over along period of time to lower the availability factor of a nuclear powerplant.

On the other hand, in the method described in Japanese Patent Laid OpenNo. Hei 6 281776, the core internals such as a core shroud and a jetpump are formed into an integral construction, and the core internalsare installed. However, the core internals described in Japanese PatentLaid Open No. Hei 6 281776 comprises a construction in which forexample, as shown in FIG. 14 of the aforesaid Publication, a piston ring55 is provided between an outer peripheral end of a baffle plate 18mounted on the end of a core shroud 2 and a reactor pressure vessel 1,which requires to change the construction itself of the reactor pressurevessel. Accordingly, there encountered a problem not capable of applyingto replacement of core internals of a reactor pressure vessel of theexisting nuclear power plant which has been already installed andoperated.

It is an object of the present invention to provide a mounting methodfor core internals capable of shortening a term of work for replacingcore internals of a reactor pressure vessel of the existing nuclearpower plant to enhance the availability factor of the nuclear powerplant.

(1) For achieving the aforementioned object, according to the presentinvention, an integrated module of core internals having a new coreshroud, a new jet pump and a new baffle plate is carried into a reactorpressure vessel in which an old baffle plate and an old shroud supportwelded and fixedly secured to the reactor pressure vessel, the newbaffle plate being fixedly secured to the old baffle plate, the new coreshroud being fixedly secured to the old shroud support.

With the method as described above, there is provided an integratedmodule having a new shroud, a new jet pump and a new baffle plate forreplacement, and the module is carried into the reactor pressure vessel,and the new baffle plate is fixed secured onto the old baffle plate.Thus, carrying in is easy and processing for removing a distortion isunnecessary, thus enabling shortening of a term of work for replacement.

(2) In the above described configuration (1), preferably, the integratedmodule of the core internals having the new shroud, the new jet pump andthe new baffle plate is carried into the reactor pressure vessel throughan opening provided on a roof of a reactor building for receiving thereactor pressure vessel.

With the method as described, since the module is carried in from theopening on the roof of the reactor building, the carrying in of dividedshrouds and the individual carrying in of constituent parts of a jetpump are unnecessary, thus being capable of shortening a term of workfor replacing core internals.

(3) In the above described configuration (1), preferably, the new jetpump comprises a new jet pump inlet mixer, a new jet pump riser, and anew jet pump diffuser, the new jet pump diffuser having a lower endfixedly secured to the new baffle plate, the new jet pump riser beingsecured to the new shroud by a new jet pump riser brace mounted on anouter wall of the new shroud.

(4) For achieving the aforementioned object, according to the presentinvention, an old core shroud and an old jet pump from an old shroudsupport and an old baffle plate from a reactor pressure vessel are cutand carried out, and an integrated module of core internals having a newcore shroud, a new jet pump and a new baffle plate is carried into areactor pressure vessel in which an old baffle plate and an old shroudsupport welded and fixedly secured to the reactor pressure vessel areleft, the new baffle plate being fixedly secured to the old baffleplate, the new core shroud being fixed secured to the old shroudsupport.

With the method as described above, it is possible to shorten a term ofwork for replacement.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a sectional view showing a constitution of a reactor buildingnear a reactor pressure vessel to which is applied a mounting method forcore internals according to a first embodiment of the present invention.

FIG. 2 is a partially sectioned perspective view showing an internalconstitution of RPV as an object for the mounting method for coreinternals according to the first embodiment of the present invention.

FIG. 3 is a partially sectioned perspective view showing a state that anold shroud and an old jet pump prior to carrying out in the mountingwork for core internals according to the first embodiment of the presentinvention are installed within RPV.

FIG. 4 is a flow chart of steps showing working steps of the mountingmethod for core internals according to the first embodiment of thepresent invention.

FIG. 5 is an explanatory view of a state of RPV in a state that the stepof Step S100 of FIG. 4 was terminated according to the first embodimentof the present invention.

FIG. 6 is an explanatory view showing a state of neighborhood of a roofand an outdoor of a reactor building in the mounting method for coreinternals according to the first embodiment of the present invention.

FIG. 7 is a perspective view showing a constitution of an integral typemodule of a shroud and a jet pump used for the mounting method for coreinternals according to the first embodiment of the present invention.

FIG. 8 is an enlarged perspective view of a portion X in FIG. 7.

FIG. 9 is an explanatory view of a carrying in state of an integral typemodule in the mounting method for core internals according to the firstembodiment of the present invention.

FIG. 10 is an explanatory view of a carrying in state of an integraltype module in the mounting method for core internals according to thefirst embodiment of the present invention.

FIG. 11 is an explanatory view of a connecting state of a new shroud anda shroud support in the mounting method for core internals according tothe first embodiment of the present invention.

FIG. 12 shows a state that a new shroud, a new jet pump and a new baffleplate are set within the reactor in the mounting method for coreinternals according to the first embodiment of the present invention.

FIG. 13 is an enlarged perspective view of a portion Y in FIG. 12.

FIG. 14 is an explanatory view of another securing method for a newbaffle plate and an old baffle plate in the mounting method for coreinternals according to the first embodiment of the present invention.

FIG. 15 is an explanatory view of a state of RPV in a state that thestep of Step S100 of FIG. 4 was terminated according to a secondembodiment of the present invention.

FIG. 16 is a perspective view showing a constitution of an integral typemodule of a shroud and a jet pump used for the mounting method for coreinternals according to the second embodiment of the present invention.

FIG. 17 is an explanatory view of a connecting state of a new shroud anda new baffle plate in the mounting method for core internals accordingto the second embodiment of the present invention.

FIG. 18 is an explanatory view of a connecting state of a new shroud anda new baffle plate in the mounting method for core internals accordingto a third embodiment of the present invention.

FIG. 19 is a flow chart of steps showing working steps of the mountingmethod for core internals according to a fourth embodiment of thepresent invention.

FIG. 20 is a perspective view showing a constitution of an integral typemodule of a new baffle plate and a new diffuser used for the mountingmethod for core internals according to the fourth embodiment of thepresent invention.

FIG. 21 is a perspective view showing a constitution of an integral typemodule of a shroud and a jet pump used for the mounting method for coreinternals according to the fourth embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

A mounting method for core internals according to a first embodiment ofthe present invention will be described hereinafter with reference toFIGS. 1 to 14.

First, the constitution of a reactor building near a reactor pressurevessel to which is applied the mounting method for core internalsaccording to the present embodiment will be described with reference toFIG. 1.

A reactor building 4 for a boiling water type reactor plant isinteriorly arranged with a pressure container vessel (hereinafter called“PCV” (Pressure Container Vessel)) 3 under the operating floor 5. PCV 3interiorly receives a reactor pressure vessel (hereinafter called “RPV”)1. The PRV1 is provided with core internals 2. The core internals 2 area construction within RPV1, and is composed of a core shroud(hereinafter called “shroud”) 11, and a jet pump 16. The shroud 11 istubular core internals surrounding a core arranged within RPV1. A jetpump 16 is arranged on the outer peripheral side of the shroud 11.

Above RPV1 are provided a reactor well 6, a fuel pool 8 for storingfuel, and an apparatus pool 7 for temporarily placing therein coreinternals such as a steam dryer removed during a periodic inspection.Further, a fuel replacing truck 9 for replacing fuel is provided on theoperating floor 5. Further, a ceiling crane 10 is provided near a roofof the reactor building 4. The ceiling crane 10 is mainly to raisemembers to be removed during the periodic inspection such as a reactorpressure vessel top head (hereinafter called “RPV top head”) 1 a, asteam dryer, and a steam separator shroud head of the core internals 2.

An apparatus carrying in inlet 4 a is provided under the reactorbuilding 4, and apparatus hatches 4 b are arranged in each floor to theoperating floor 5. An opening 55 is provided above the reactor building4 and above RPV1. The opening 55 has the size enough to carry out oldcore internals 2 to be replaced or to carry in core internals to bemounted newly. A closable door 51 is installed on the opening 55.

Next, the internal constitution of RPV to be an object of the mountingmethod for an in-pile construction according to the present embodimentwill be described with reference to FIG. 2.

The shroud 11 is arranged in a central portion within RPV1 and supportedby a shroud support cylinder 12. The shroud support cylinder 12 issupported on the bottom of RPV1 by a baffle plate 28 and a shroudsupport leg 13.

The shroud 11 is interiorly provided, at an upper part, with an upperlattice plate 14 as an upper core support plate, and at a lower part,with a core support plate 15 as a lower core support plate. Further, acontrol rod 20 and a fuel assembly 21 are installed internally of theshroud 11.

A jet pump 16 is provided between the shroud 11 and RPV1. The jet pump16 comprises a jet pump inlet mixer (hereinafter called “inlet mixer”)17, a jet pump riser (hereinafter called “riser”) 18, a jet pumpdiffuser (hereinafter called “diffuser”) 19, and an instrumentation line(hereinafter called “sensing line”) 19 a. The riser 18 has one endconnected to a thermal sleeve 26 a of a recirculation inlet nozzle 26,and the other end connected to the inlet mixer 17. The diffuser 19 hasone end mounted on the baffle plate 28 and the other end connected tothe inlet mixer 17. The baffle plate 26 is formed, at a mounting portionrelative to the diffuser 19, with a hole 28 a through which reactorwater passes. One (or two) sensing line(s) 19 a is extended out of eachdiffuser 19 for the purpose of measuring pressure, and is connected toan out pile line by an instrumentation nozzle through the inner side ofa group of diffusers.

Above the shroud 11 are provided a steam dryer 24, steam separatorshroud heads 25, a guide rod 31, a feedwater sparger 22, and a corespray sparger 23.

Next, a description will be made, with reference to FIG. 3, of a statethat an old shroud 11 and an old jet pump 16 prior to carrying out inthe mounting work for core internals according to the present embodimentare installed in PRV1. It is noted that the same reference numerals asthose of FIG. 2 denote the same parts.

The cylindrical shroud support cylinder 12 is secured on the shroudsupport leg 13 supported on the bottom of RPV1 by welding or the like.In the inner peripheral side of the ring like baffle plate 28, theshroud support cylinder 12 is secured to the outer peripheral surfacethereof by welding or the like, and the outer peripheral side is securedto the inner peripheral surface of RPV1 by welding or the like. Theshroud 11 is secured by welding or the like too the shroud supportcylinder 12.

The jet pump 16 is provided between the shroud 11 and RPV1. The jet pump16 comprises the inlet mixer 17, the riser 18, and the diffuse 19. Thejet pump 16 is secured to the inner wall of RPV1 by a jet pump riserbrace (hereinafter called “riser brace”) 18 a. The riser 18 has one endconnected to a thermal sleeve 26 a of a recirculation inlet nozzle 26and the other end connected to the inlet mixer 17. The diffuser 19 hasone end mounted on the baffle plate 28 and the other end connected tothe inlet mixer 17. The baffle plate 28 is formed, at a mounting portionrelative to the diffuser 19, with a hole 28 a through which reactorwater passes.

Next, working steps of the mounting method for core internals accordingto the present embodiment will be described with reference to FIGS. 4and 5 to 14.

First, in Step S100 in FIG. 4, old core internals to be replaced such asthe old shroud 11 and the old jet pump 16 within RPV1 are carried out.To be more specific, the shroud 11 is carried out in such a manner thatit is cut in a connecting portion A relative to the shroud supportcylinder 12 shown in FIG. 3. The old jet pump 16 is carried out in sucha manner that the riser brace 18 a is removed, a connecting portion Bbetween the riser 18 and the nozzle thermal sleeve 26 a of therecirculation inlet 26 is cut, and the diffuser 19 is separated from thebaffle plate 28.

The old core internals to be replaced such as the old shroud 11 and theold jet pump 16 are disassembled, and then carried out from theapparatus hatches 4 b and the apparatus carrying in inlet 4 a by theceiling crane 10 as shown in FIG. 1. It is also possible to carry outthem from the opening 55 while remaining large in size without beingdisassembled, as will be described later.

Next, a description will be made, with reference to FIG. 5, of a stateof RPV1 in a state that the step of Step S100 in FIG. 4 has, beenterminated.

When the step of Step S100 in FIG. 4 is terminated, the core internalssuch as the old shroud 11 and the old jet pump 16 are carried out, andwithin the RPV1 remain the shroud support cylinder 12, the baffle plate28, the shroud support leg 13, and brackets such as a guide supportbracket 31 a, a feedwater sparger support bracket 22 a, and a core spraysparger support bracket 23 a.

In the drawing, a portion A is a cut portion between the shroud 11 andthe shroud support cylinder 12, and in the drawing, a portion B is a cutportion between the riser 18 and the nozzle thermal sleeve 26 a of thereciculatiion inlet 26.

That is, in the present embodiment, when the old core internals (the oldshroud 11 and the old jet pump 16) are carried out, the baffle plate 28,the shroud support cylinder 12 and the shroud support leg 13 are to beleft. Since the baffle plate 28 and the shroud support cylinder 12 aredirectly connected to the wall surface of RPV1, when the baffle plate 28and the shroud support cylinder 12 are separated from the RPV1 and thencarried out, there is a possibility that are necessary post processingfor removing a distortion generated by cutting, and heat treatment forremoving stress and distortion generated by welding after a new baffleplate and a new shroud support cylinder have been newly welded andsecured to RPV1. When these processings are carried out, the workingtime is extended over a long period of time and work is to be done underhigh radiation dose, because of which the exposure rate of workersincreases, whereas the baffle plate 28 and the shroud support cylinder12 are to be left as described above whereby the work time forreplacement can be shortened, and the exposure rate of workers can bereduced.

Next, in Step S101 in FIG. 4, in order that a new jet pump is easily setwithin the reactor, positions of the recirculation inlet nozzle 26 andthe baffle plate hole 28 a in which a new riser is joined with a newdiffuser are measured to be reflected on the dimension when the new jetpump and the new shroud are assembled.

Next, in Step S102, as shown in FIG. 6, the closable door 51 provided onthe ceiling of the reactor building 4 is moved to open the opening 55,and a crane 50 is installed in the vicinity of outdoor of the reactorbuilding 4.

Next, in Step 103 in FIG. 4, brackets left within RPV are cut andremoved side by side with Step S102. That is, brackets such as the guiderod support bracket 31 a , the feedwater sparger support bracket 22 a,and the core spray sparger support bracket 23 a left within RPV1 shownin FIG. 5 are cut and removed where they interfere when an integratedmodule of a new shroud and a new jet pump described later are carriedin.

Next, in Step 104 in FIG. 4, the integrated module having a new shroudand a new jet pump is carried in the reactor building 4 and carried inRPV1 through the opening 55 of the reactor building 4 using a craneshown in FIG. 6.

The constitution of the integrated type module of a shroud and a jetpump used in the mounting method for core internals according to thepresent embodiment will be described with reference to FIGS. 7 and 8.FIG. 8 shows a state that the portion X in FIG. 7 is enlarged.

A new riser brace N18 a is mounted on the outer wall of a new shroudN11, as shown in FIG. 8, to fix a new riser N18. The lower end of a newdiffuser N19 is fixed secured to airing like new baffle plate N29. Thenew baffle plate N29 is formed, at a mounting portion relative to thediffuser N19, with a hole through which reactor water passes. The upperend of the new diffuser N19 and the upper end of the new riser N18 arerespectively secured to a new inlet mixer N17. A space Z is formedbetween the lower end N11Z of the new shroud 11 and the inner peripheralside of the new baffle plate N29. When the sensing line 19 a isincorporated into the module, it is fixed to a diffuser, but details ofthe range and mounting method thereof are determined by the executionmethod of the sensing line 19 a.

With the constitution described above, the new jet pump N16 comprisingthe new inlet mixer N17, the new riser N18 and the new diffuser N19constitutes the integrated module with the new shroud N11 together withthe new baffle plate N29.

Further, a belt 40 is mounted externally of the new riser N18. Where theintegrated module having the new core shroud N11 and the new jet pumpN16 interferes with the brackets such as the guide rod support bracket31 a mounted on the inner wall of RPV1 when the module is carried inRPV1, the belt 40 is tightened and the new riser N18 is moved toward thenew shroud N11 to avoid an interference with the brackets, whereby themodule can be carried into RPV. After carrying in, the belt 40 isremoved.

Where the interference between the brackets and the integrated typemodule newly carried in can be avoided by using the belt 40, theaforementioned Step S103, and Step S106 described later can be omitted.

Next, the state of carrying in of the integrated type module in th emounting method for core internals according to the present embodimentwill be described with reference to FIGS. 9 and 10.

As shown in FIG. 9, the door 51 provided on the reactor building 4 ismoved in a direction indicated by arrow M to open the opening 55. Theintegrated module comprising the new shroud N11 and the new jet pump N16is raised by the crane 50, and is carried into the reactor building 4from the opening 55 of the reactor building 4.

As shown in FIG. 10, the opening 55 has an aperture enough to carry inthe integrated module comprising the new shroud N11 and the new jet pumpN16 without interference, and the module is carried into the reactorbuilding 4 from the opening 55 of the reactor building 4 and set withinRPV1, using the crane 50.

Where in carrying out of the old shroud and the old jet pump in StepS100, the old shroud and the old jet pump are carried out without beingdisassembled, the steps of installing the roof opening and installingthe crane in Step S100 can be carried out prior to Step S100, wherebythe old shroud and the old jet pump can be also carried out from theopening of the reactor building using the crane.

Next, in Step S105, the door 51 provided on the ceiling of the reactorbuilding 4 is moved to close the opening 55, and the crane 50 installedin the vicinity of roof of the reactor building 4 is disassembled andremoved.

Next, in Step S106, the brackets such as the guide rod support bracket31 a within RPV cut and removed in Step S103 are welded and restoredside by side with Step S105. Where an interference between an integratedtype module newly carried in and the brackets can be avoided by usingthe belt 40 explained in FIG. 7, Step S106 can be omitted.

Next, in Step S107, the new shroud N11 and the shroud support cylinder12 are connected by welding.

The connecting state of a new shroud and a shroud support in themounting method for core internals according to the present embodimentwill be described with reference to FIG. 11. The same reference numeralsas those in FIGS. 5 and 7 indicate the same parts.

The module having the new shroud N11 and the new jet pump N16 integratedis installed on the shroud support cylinder 12, and the lower end of thenew shroud N11 and the upper end of the shroud support cylinder 12 areconnected by welding at a connecting portion C.

Next, in Step S108, the new baffle plate N29 and the old baffle plate 28shown in FIG. 11 are fixedly secured.

The securing state of the new baffle plate 29 and the old baffle plate28 will be described with reference to FIGS. 12 an 13.

FIG. 12 is an explanatory view of a state that the new shroud N11, thenew jet pump N16 and the new baffle plate N29 are set within the reactorin the mounting method for core internals according to the firstembodiment of the present invention. FIG. 13 is an enlarged perspectiveview of a portion Y in FIG. 12.

As shown in FIG. 12, the new shroud N11 is connected to the shroudsupport cylinder 12 by welding at a connecting portion C. The new baffleplate N29 is installed on the old baffle plate 28.

As shown in FIG. 13, the new baffle plate N29 and the old baffle plate28 are fixedly secured by welding at a welding portion 31.

Next, another securing method of the new baffle plate N29 and the oldbaffle plate 28 in the present embodiment will be described withreference to FIG. 14.

As shown in FIG. 14, the new baffle plate N29 and the old baffle plate28 are fixedly secured by means of a bolt 30.

Next, in Step S109, as shown in FIG. 12, the new riser N18 and thethermal sleeve 26 a of the recirculation inlet nozzle 26 are connectedat a connecting portion D. Fine adjustment of positions of the new riserN18 and the recirculation inlet nozzle 26 can be attained by providing atolerance in a longitudinal direction of the thermal sleeve 26 a.

As described above, according to the present embodiment, since the newshroud, the new jet pump and the new baffle plate for replacement areintegrated into a module, and the module is carried in from the openingof a roof of the reactor building, the divided carrying in of a shroudand the individual carrying in of components of a jet pump as in priorart are unnecessary, and a term of period for replacing core internalscan be shortened. Accordingly, the availability factor of nuclear powerplant can be enhanced.

Further, since the jet pump is also constituted integrally and thencarried into the reactor to reduce the assembling work within thereactor, a simple in pile shield will suffice, the number of steps ofinstalling and disassembling an in pile shield can be considerablyreduced, and a period of work in the reactor can be shortened, thusenabling reduction in exposure dose of workers to less than a half.

Further, unlike the method described in Japanese Patent Laid Open No.Hei 6 281776, the construction itself of the reactor pressure vesselneed not be changed but the present embodiment can be applied toreplacement of core internals of a reactor pressure vessel of theexisting nuclear power plant which is already installed and beingoperated.

Further, in cutting and removing the old shroud and the old jet pump,thy baffle plate and the shroud support leg constituting a pressureboundary are to be left by being welded and secured to the reactorpressure vessel, and the new baffle plate is fixedly secured to the oldbaffle plate. Therefore, processing for removing a distortion and heattreatment for removing stress and distortion are unnecessary to therebyenable shortening a term of work for replacement.

A term of work from carrying in to completion of installation can beshortened by about 30% as compared with the conventional method in whicha shroud is divided into two parts and carried in, and a jet pump iscarried in every component.

Next, a method for mounting core internals according to a secondembodiment of the present invention will be described with reference toFIGS. 15 to 17.

The work steps for the mounting method for core internals according tothe second embodiment are similar to the flow chart shown in FIG. 4. Thepresent embodiment is different in 1) the shape of a construction lefton the RPV side when the old shroud and the old jet pump are cut andremoved, and different from that shown in FIG. 7 in 2) a constitution ofa module integrated by a new shroud, a new jet pump, and a new baffleplate carried into RPV in Step S104 of FIG. 4.

First, a description is made of a state of RPV1 in a state that the stepof Step S100 of FIG. 4 has been terminated, with reference to FIG. 15.The same reference numerals in FIG. 5 indicate the same parts.

When Step S100 in FIG. 4 is terminated, the core internals such as theold shroud 11 and the old jet pump 16 are removed, and within RPV1 areleft a shroud support cylinder 12′, a baffle plate 28, and a shroudsupport leg 13, and brackets such as a guide rod support bracket 31 a, afeedwater sparger support plate 22 a, and a core spray sparger supportbracket 23 a. These constructions are not to be replaced.

In the example shown in FIG. 5, in the connecting portion of the shroud11 and the shroud support cylinder 12, cutting is made, whereas in thepresent embodiment, the shroud support cylinder 12′ is cut at a positionhalfway of the shroud support cylinder 12′, that is, at a position ofthe same height as the upper end of the baffle plate 28. In the figure,a portion A′ is a cutting portion of the shroud support cylinder 12′,and a portion B is a cutting portion between the riser 18 and the nozzlethermal sleeve 26 a of the recirculation inlet 26.

Next, a description is made of a constitution of an integrated typemodule of a shroud and a jet pump used in the mounting method for coreinternals according to the present embodiment, with reference to FIG.16.

The same reference numerals in FIG. 7 indicate the same parts.

A new riser brace N18 a is mounted on the outer wall of a new shroudN11′ to fix a new riser N18. A new diffuser N19 is fixedly secured to aring like new baffle plate N29′ at the lower end thereof. The new baffleplate N29′ is formed, at a mounting portion of the new diffuser N19,with a hole through which reactor water passes. The upper end of the newdiffuser N19 and the upper end of the new riser N18 are respectivelysecured to a new inlet mixer N17.

In the example shown in FIG. 7, the space Z is formed between the lowerend N11Z of the new shroud N11 and the inner peripheral side of the newbaffle plate N29, whereas in the present embodiment, the lower end ofthe new shroud N11′ and the inner peripheral side of the new baffleplate N29′ are connected by welding. Accordingly, centering between thenew shroud N11′ and the new baffle plat N29′ is easy. Further, settingof the new diffuser N19 and the new baffle plate N29′ is easy.

With the above described constitution, a new jet pump 16N comprising thenew inlet mixer N17, the new riser N18, and the new diffuser N19constitutes a module integrated with the new shroud N11′ together withthe new baffle plate N29′.

Next, a securing state of the new baffle plate N29 and the old baffleplate 28 will be described with reference to FIG. 17.

The new shroud N11′ is connected to the shroud support cylinder 12 at aconnecting portion C′ by welding. The new baffle plate N29 is installedon the old baffle plate 28. The new baffle plate N29 is fixedly securedto the old baffle plate 28 at a welding portion 31′ by welding.Accordingly, setting of a hole 28 a of the old diffuser 28 and a holeN29 a of the new baffle plate N29 is easy.

As described above, according to the present embodiment, since the newshroud, the new jet pump, and the new baffle plate for replacement areintegrated into a module, and the module is carried in from the openingof a roof of the rector building, the divided carrying in of the shroudand the individual carrying in of components of the jet pump in theprior art are unnecessary to enable shortening of a term of work forreplacement of core internals. Accordingly, it is possible to enhancethe availability factor of a nuclear power plant.

Further, since the jet pump is integrally constituted and then carriedinto the reactor, which is less in assembling work within the reactor, asimple in pile shield will suffice, the number of steps for installingand disassembling an in pile shield can be considerably reduced, and aterm of work in the reactor can be shortened to enable reduction inexposure dose of workers to less than a half.

The construction itself of the reactor pressure vessel need not bechanged but the present embodiment can be applied to replacement of coreinternals of a reactor pressure vessel of the existing nuclear powerplant which is already installed and being operated.

Further, in cutting and removing the old shroud and the old jet pump,the baffle plate and the shroud support leg constituting a pressureboundary are to be left by being welded and secured to the reactorpressure vessel, and the new baffle plate is fixedly secured to the oldbaffle plate. Therefore, processing for removing a distortion and heattreatment for removing stress and distortion are unnecessary to therebyenable shortening a term of work for replacement.

Next, a mounting method for core internals according to a thirdembodiment of the present invention will be described with reference toFIG. 18.

The work steps of a mounting method for core internals according to thepresent embodiment are similar to the flow chart for steps shown in FIG.4. In the present embodiment, the constitution of the module integratedby the new shroud, the new jet pump and the new baffle plate carriedinto RPV in Step S104 of FIG. 4 is different from that shown in FIG. 7.

The state of RPV1 in a state that the step of Step S100 in FIG. 4 hasbeen terminated is similar to that shown in FIG. 5. That is, cutting iseffected at a connecting portion of the shroud 11 and the shroud supportcylinder 12.

Further, a constitution of an integrated type module of a new shroud anda new jet pump is similar to that shown in FIG. 16. That is, as shown inFIG. 16, the lower end of the new shroud N11′ and the inner peripheralside of the new baffle plate N29′ are connected by welding. It is notedthat the inside diameter of the new shroud N11′ is slightly larger thanthe outside diameter of the shroud support cylinder 12.

A securing state of a new baffle plate N29 and an old baffle plate 28will be described with reference to FIG. 18.

The inside diameter R2 of the new shroud N11′ is slightly larger thanthe outside diameter R1 of the shroud support cylinder 12, and the upperend of the shroud support cylinder 12 is inserted into the new shroudN11′ whereby the new shroud 11′ is installed.

The new shroud N11 is connected to the shroud support cylinder 12 at aconnecting portion C″ by welding. The new baffle plate N29 is installedon the old baffle plate 28. The new baffle plate N29 is fixedly securedto the old baffle plate 28 at a welding portion 31′ by welding.Accordingly, setting of the old baffle plate 28 and the new shroud N11′is further easier.

As described above, according to the present embodiment, since the newshroud, the new jet pump, and the new baffle plate for replacement areintegrated into a module, and the module is carried in from the openingof a roof of the reactor building, the divided carrying in of a shroudand the individual carrying in of components of a jet pump in the priorart are unnecessary to enable shortening of a term of work forreplacement of core internals. Accordingly, it is possible to enhancethe availability factor of a nuclear power plant.

Further, since the jet pump is integrally constituted and then carriedinto the reactor, which is less in assembling work within the reactor, asimple in pile shield will suffice, the number of steps for installingand disassembling an in pipe shield can be considerably reduced, and aterm of work in the reactor can be shortened to enable reduction inexposure dose of workers to less than a half.

The construction itself of the reactor pressure vessel need not bechanged but the present embodiment can be applied to replacement of coreinternals of a reactor pressure vessel of the existing nuclear powerplant which is already installed and being operated.

Further, in cutting and removing the old shroud and the old jet pump,the baffle plate and the shroud support leg constituting a pressureboundary are to be left by being welded and secured to the reactorpressure vessel, and the new baffle plate is fixedly secured to the oldbaffle plate. Therefore, processing for removing a distortion and heattreatment for removing stress and distortion are unnecessary to therebyenable shortening a term of work for replacement.

Next, a mounting method for core internals according to a fourthembodiment of the present invention will be described with reference toFIGS. 19 to 21.

First, the mounting method for core internals according to the fourthembodiment will be described with reference to FIG. 19.

In the work steps according to the present embodiment, the same steps asthose shown in FIG. 4 indicate the same work steps. In the presentembodiment, the work steps S204, S205, and S206 are carried out in placeof Step S104, and S108 shown in FIG. 4.

First, in Step S204 of FIG. 19, an integrated module having a new baffleplate and a new diffuser is carried into RPV through an opening 55 of areactor building 4 by a crane 50 installed externally of the reactorbuilding 4, similarly to those shown in FIGS. 9 and 10.

A constitution of an integrated module of a new baffle plate and a newdiffuser used in the mounting method for core internals according to thepresent embodiment will be described with reference to FIG. 20.

A new diffuser N19 is fixedly secured to a ring like new baffle plateN29 at the lower end thereof. The new baffle plate N29 is formed, at amounting portion relative to the new diffuser N19, with a hole throughwhich reactor water passes.

With the above described constitution, an integrated module having thenew baffle plate N29 and the new diffuser N19 is constituted.

Next, in Step 205 of FIG. 19, the new and old baffle plates are fixedlysecured. That is, as shown in FIG. 13, the new baffle plate N29 isinstalled on the old baffle plate 28, and the new baffle plate N29 andthe old baffle plate 28 are fixedly secured at a welding portion 31 bywelding. Alternatively, as shown in FIG. 14, the new baffle plate 29 andthe old baffle plate 28 are fixedly secured by means of a bolt 30.

Next, in Step 206 of FIG. 19, an integrated module having a new shroud,a new riser and a new inlet mixer is carried into the reactor.

Now, a constitution of an integrated type module of a shroud and a jetpump used in the mounting method for core internals according to thepresent embodiment will be described with reference to FIG. 21.

A new riser brace N18 a is mounted on the outer wall of a new shroud N11to fix a new riser N18. With the above mentioned construction, a newinlet mixer N17 is secured to the upper end of the new riser N18. A newjet pump comprising the new inlet mixer N17 and the new riser N18constitutes an integrated module with the new shroud N11.

A belt 40 is mounted externally of the new riser N28. Where theintegrated module having the new core shroud N11 and the new jet pumpinterferes with brackets such as a guide rod support bracket 31 amounted on the inner wall of RPV1 when the module is carried into RPV1,the belt 40 is tightened to move the new riser N18 toward the new shroudN11 to avoid the interference with the brackets, thus enabling carryingin the module into RPV. After carrying in, the belt 40 is removed.

Where the interference of the brackets with the integrated type modulenewly carried in can be avoided by using the belt 40, the aforementionedstep S103 and Step S106 described later can be omitted.

This module is carried into the reactor through an opening 55 of areactor building 4 by a crane 50 installed externally of the reactorbuilding 4. Alternatively, the new inlet mixer N17 can be carried intothe reactor with the new shroud N11 and the new riser N18 integrated,and then mounted. Where no interference with the apparatus carrying inhatch occurs, and where no short in capacity of the ceiling crane 10 ofthe reactor building or no short in suspending allowance of the ceilingcrane 10 occurs when the integrated module having the new diffuser N19and the new baffle plate N29, and the integrated module having the newshroud N11, the new riser N18 and the new inlet mixer N17 are carriedinto the reactor building 4, Step S102 and Step S105 can be omitted.

Further, the baffle plate can be divided into three parts or more tothereby enable avoidance of interference relative to the core internalswall bracket for carrying in.

As described above, according to the present embodiment, the integratedmodule having the new diffuser and the new baffle plate for replacement,and the integrated module having the new shroud, the new riser and thenew inlet mixer are carried in through the opening of a roof of thereactor building. Therefore, the divided carrying in of a shroud and theindividual carrying in of components of a jet pump in the prior art areunnecessary to enable shortening of a term of work for replacement ofcore internals. Accordingly, the availability factor of a nuclear powerplant can be enhanced.

Further, the jet pump is also integrated and then carried into thereactor to reduce the assembling work within the reactor. Thereby, asimple in pile shield will suffice, the number of steps for installingand disassembling an in pile shield can be considerably reduced, and aterm of work in the reactor can be shortened to reduce the exposure doseof workers to less than a half.

Further, the construction itself of the reactor pressure vessel need,notbe changed but the present embodiment can be applied to replacement ofcore internals of a reactor pressure vessel of the existing nuclearpower plant which is already installed and being operated.

Further, in cutting and removing the old shroud and the old jet pump,the baffle plate and the shroud support leg constituting a pressureboundary are to be left by being welded and secured to the reactorpressure vessel, and the new baffle plate is fixedly secured to the oldbaffle plate. Therefore, processing for removing a distortion and heattreatment for removing stress and distortion are unnecessary to therebyenable shortening a term of work for replacement.

In the above described description, the first to third embodiments areconstituted by an integrated module having a new shroud, a new jet pumpand a new baffle plate for replacement. The fourth embodiment isconstituted by an integrated module having a new diffuser and a newbaffle plate for replacement and an integrated module having a newshroud, a new riser and a new inlet mixer. Any of these embodiments areincluded in a concept of an integrated module having a new shroud, a newjet pump and a new baffle plate for replacement according to the presentinvention.

INDUSTRIAL APPLICABILITY

According to the present invention, it is possible to shorten a term ofwork for replacement of core internals of a reactor pressure vessel ofan existing nuclear power plant to enhance the availability factor ofthe nuclear power plant.

What is claimed is:
 1. A mounting method for core internals, comprisingthe steps of: carrying an integrated module of core internals having anew core shroud, a new jet pump and a new baffle plate into a reactorpressure vessel in which an old baffle plate and an old shroud supportcylinder welded and fixedly secured to the reactor pressure vessel andan old shroud support leg fixedly secured to said old baffle plate andsaid old shroud support cylinder are left; fixedly securing said newbaffle plate to said old baffle plate; and fixedly securing said newcore shroud to said old shroud support cylinder.
 2. The mounting methodfor core internals according to claim 1, wherein said integrated moduleof core internals having the new core shroud, the new jet pump and thenew baffle plate is carried into said reactor pressure vessel through anopening provided in a roof of a reactor building for receiving saidreactor pressure vessel.
 3. The mounting method for core internalsaccording to claim 1, wherein said new jet pump comprises a new jet pumpinlet mixer, a new jet pump riser and a new jet pump diffuser; a lowerend of said new jet pump diffuser is fixedly secured to said new baffleplate; and said new jet pump riser is secured to said new shroud by anew jet pump riser brace mounted on an outer wall of said new shroud. 4.A mounting method for core internals, comprising the steps of: cuttingan old core shroud and an old jet pump from an old shroud supportcylinder and an old baffle plate and carrying the old core shroud andthe old jet pump out from a reactor pressure vessel; carrying anintegrated module of core internals having a new core shroud, a new jetpump and a new baffle plate into the reactor pressure vessel in whichthe old baffle plate and the old shroud support cylinder welded andfixedly secured to the reactor pressure vessel, and said old baffleplate and said old shroud support cylinder are left; fixedly securingsaid new baffle plate to said old baffle plate; and fixedly securingsaid new core shroud to said old shroud support cylinder.